Provide support for new chips with multiple inbound windows while
keeping the legacy support for the older chips.
In existing chips there are three inbound windows with fixed purposes: the
first was for mapping SoC internal registers, the second was for memory,
and the third was for memory but with the endian swapped. Typically, only
one window was used.
Complicating the inbound window usage was the fact that the PCIe HW would
do a baroque internal mapping of system memory, and concatenate the regions
of multiple memory controllers.
Newer chips such as the 7712 and Cable Modem SOCs take a step forward and
drop the internal mapping while providing for multiple inbound windows.
This works in concert with the dma-ranges property, where each provided
range becomes an inbound window.
Signed-off-by: Jim Quinlan <james.quinlan@xxxxxxxxxxxx>